While the English language only has one word for “memory,” the truth is that memory comes in many different forms. Psychologists break memory down into dozens of categories: long-term memory, short-term memory, implicit memory and declarative memory. But this concept expands beyond the individual human mind. For example, history itself is a kind of memory.
Just as our personal existence would make little sense without memories to put the present into context, our cultural existence would also seem meaningless without traditions or an understanding of the past.
Like an amnesic patient who has difficulty mapping out a future without a solid understanding of the past, a society that forgets easily is in danger of repeating past mistakes. Unfortunately, some of the most crippling neurological disorders impact memory. The first step in developing treatments for these disorders is to arrive at a biological understanding of how memories are formed and stored.
No scientist has brought us closer to this kind of an understanding of memory than Eric Kandel. But before going into his contributions to neuroscience, it is crucial to note the historical context behind Kandel’s story.
Before he was even interested in neuroscience, Kandel was a Jewish boy living in Vienna, Austria, when Adolf Hitler invaded the country in 1938. While Hitler technically took over Austria during World War II, his presence was embraced by a number of Austrians. Austria had harbored quite an anti-Semitic atmosphere in the 1930s, and Kandel and his family were lucky to leave before World War II officially began.
They migrated to New York, where Kandel began studying psychoanalysis, influenced by Viennese scientist Sigmund Freud. While he remained interested in the subject matter, his interests began to gravitate toward neurobiology. Specifically, he sought to understand memory at the cellular level. He studied marine mollusks called Aplysia and observed the physical changes that occur in their neurons as they learned.
What can mollusks teach us about memory and behavior? They have tube-like structures called siphons that, when touched, cause them to withdraw their gills in defense. However, if touched repeatedly, the invertebrate eventually learns that the touch isn’t dangerous. Thanks to a process called habituation, mollusks withdraw their gills less and less. In addition, if you shock their tails, the animals quickly learn to be more careful and begin to withdraw their gills as much as they did before habituation, a process called sensitization.
Kandel found that those shocks triggered a set of neurons to release serotonin that eventually causes the muscles surrounding the gill to move. The serotonin makes these neurons more active, so that the mollusk reverts back to responding quickly to the siphon touches. In essence, there is a vestigial appearance of memory in the response.
Interestingly, repeated tail shocks over the course of days vastly reduce the mollusk’s tendency to habituate. But how is it that the mollusk can keep track of what happens to it throughout long periods of time? The easy answer is that it “remembers.” But what does that look like physically?
Kandel demonstrated that the repeated shocks activate genes that strengthen the connections between neurons in the circuit. In other words, he demonstrated that long-term memory in mollusks — and potentially humans — depends on gene expression to bolster connections between neurons.
Kandel’s research had important implications for how we understand not just what memory is, but the role it plays in our lives. For Kandel, the memory of Nazi Germany left him great trauma, but served as an experience that led to the identification of pioneering work in long-term memory related to biological adaptation and gene expression. For the rest of us, his work showed the intricate and complex nature of memories and the role they play in our daily lives.
Ayan Mandal is a junior in the College. This is the final installment of Brain History.
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